As described in, for example, PTL 1, various components such as a shutoff valve are mounted in a gas meter.
FIG. 8 is a cross-sectional view illustrating a conventional gas meter 100. The gas meter 100 is provided with an opening portion 200a used as an inflow port of gas and an opening portion 200b used as an outflow port of gas. A shutoff valve 700 is mounted to the opening portion 200a via a shutoff valve adaptor 600. A measuring unit 900 is mounted to the opening portion 200b via a measuring unit adaptor 800.
FIG. 9 is a plan view illustrating the shutoff valve adaptor 600 and the shutoff valve 700 mounted to the shutoff valve adaptor 600 as seen from direction E in FIG. 8. A flange portion 600a of the shutoff valve adaptor 600 is provided with two through-holes 600b. The shutoff valve adaptor 600 is mounted to the opening portion 200a by screwing (a screw 300 as illustrated in FIG. 8) using these through-holes 600b. 
In addition, FIG. 10 is a plan view illustrating the measuring unit adaptor 800 and the measuring unit 900 mounted to the measuring unit adaptor 800 as seen from direction E in FIG. 8. A flange portion 800a of the measuring unit adaptor 800 is provided with two through-holes 800b. The measuring unit adaptor 800 is mounted to the opening portion 200b by screwing (a screw 400 as illustrated in FIG. 8) using these through-holes 800b. 